Momentum can matter immensely in tennis, which races through the season almost without pause.  Momentum certainly seemed to aid Spanish journeyman Guillermo Garcia-Lopez in Monte Carlo, where he built on a title in Casablanca last week by upsetting Tomas Berdych.

Best known for upsetting Rafael Nadal in Bangkok and Andy Murray at Indian Wells, Garcia-Lopez has spent most of his career in the shadow of more famous compatriots.  The world No. 38 had won just two titles before claiming Casablanca on Sunday with a three-set comeback against Marcel Granollers.  He would mount another comeback against Berdych after losinga  break-strewn first set.

Capitalizing on his opponent's dismal first-serve percentage, Garcia-Lopez lost just four games over the last two sets.  As was the case in his previous upsets over Nadal and Murray, he dominated behind his own serve throughout that span.  Garcia-Lopez faced only two break points in the second and third sets combined, saving both of them.  Across the net, Berdych's first serve inexorably declined in accuracy.  He had struggled at times on serve in his first match against Dmitry Tursunov, trailing midway through both sets.  This time, Berdych could not escape a steadier, more confident foe.

Garcia-Lopez will need all of the confidence that he can find in a quarterfinal against defending champion Novak Djokovic.  He will enter that match as a heavy underdog despite his top-10 upset on Thursday.  Not only has Djokovic won all of his previous meetings with the Spaniard, whereas Berdych had split four with Garcia-Lopez, but his dominance this week has been staggering.  The defendig champion has lost two total games in two matches, spending barely 90 minutes on court between them.

That said, the 38th-ranked Garcia-Lopez marks a significant step up in competition for Djokovic, who faced a qualifier and a lucky loser in his two previous routs.  The Serb cannot afford to take the Spaniard lightly as he pursues his 23rd consecutive Masters 1000 victory.

Most of the other favorites in Monte Carlo advanced routinely on Thursday, which witnessed straight-sets wins by Rafael Nadal, Roger Federer, and David Ferrer.  Stanislas Wawrinka received a walkover from Nicolas Almagro and has reached the quarterfinals after spending just 46 minutes on court.  Slightly more surprising were the victories of two fast-court specialists, Milos Raonic and Fabio Fognini, over a pair of clay specialists in Tommy Robredo and Fabio Fognini, respectively.  A semifinalist in Monte Carlo last year, Fognini absorbed a blow in his quest to crack the top 10 for the first time.  

While Raonic will set his sights on Wawrinka, Tsonga will seek to repeat his clay upset of Federer at Roland Garros in 2013.  Ferrer will face Nadal in a rematch of last year''s Roland Garros final as he seeks to solve his compatriot on clay for the first time in nearly a decade.  And Garcia-Lopez will target his first Masters 1000 semifinal against a man aiming for his fifth straight Masters 1000 title.